Now we know how hot things got when the universe was born. We've taken the temperature of a substance that only existed when time first began. It's an ultrahot, 4-trillion degree "soup" of subatomic particles made from gold.

The Relativistic Heavy Ion Collider (RHIC) has succeeded in smashing together gold ions, producing the soup of subatomic quarks and gluons and mimicking conditions at the start of the universe.

The research group recently announced some of their findings from the magnificent explosion that occurs when gold collides, which will be published in full in Physical Review Letters. The ions are accelerated to such speed that the impact creates matter of such high temperature that protons and neutrons melt down into their constituent parts: a plasma of quarks and gluons.

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The temperature reaches an astonishing four trillion degrees Celsius, but for an incomparably brief period of time. The experiment reaches that level of heat for less time than it takes light to travel across a single proton — a billionth of a trillionth of a second. Under this extreme heat, a freely flowing liquid composed of quarks and gluons is created. This "soup" is thought to have filled the universe for fractions of a second after its creation, before cooling into protons and neutrons.

How do you measure something 250,000 times as hot as the center of the sun, but that only exists for a fraction of a second? The scientists observe the color and energy distribution of the light that the reaction creates, which gives them sufficient information to correctly judge the temperature, even when hotter than anything previously created in a laboratory.

Before the RHIC was fired up, it was widely believed that the resulting quark-gluon mixture would behave as a gas, but their current information — first presented in 2005 — shows that it behaves more like a liquid, "whose constituent particles interact very strongly among themselves". This liquid has been described as "perfect", because it has almost no friction or viscosity.

The RHIC is an atom smasher located at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory, that first managed to collide together the gold particles in 2005. Since then, they've been working to better understand what happens in the extremely brief aftermath, to help better understand the nature of the universe.

Over the next few years, the BNL plans to upgrade the RHIC to increase its collision rate and improve the sensors, in order to better analyze the smallest known components of matter.